The present invention relates to material removing tools in general, and more particularly to improvements in material removing tools which can be used in mining and other material removing machines. Still more particularly, the invention relates to improvements in material removing tools of the type wherein a holder is provided with a chamber for the shank of a bit and the shank is releasably held in the chamber by a cotter, a wedge or the like.
The tool which is used in the mining machine for removal of coal or another mineral from the face of a mine in an underground excavation or in surface mining normally comprises a bit with a cutting edge which comes into actual contact with the material to be removed. The bit has a solid shank extending into the chamber of a holder which is removably or permanently secured to the conveyor of the machine, such as an endless chain, a wheel or the like. Means is provided for releasably attaching the bit to the holder so as to ensure that the shank will remain in the chamber while the cutting edge of the bit removes material from the mine face. It is also known to employ screws, bolts or other threaded elements which releasably secure the bit to its holder.
A drawback of many conventional bit and holder combinations is that the attachment of the bit to, or its detachment from, the holder is a time-consuming operation which often requires the utilization of specially designed tools. On the other hand, it is desirable to ensure that the bit can be readily detached from its holder because the useful life of the bit is much shorter than that of the holder. Since such replacement of bits often takes place in an underground excavation where the illumination is unsatisfactory, the establishment of a reliable but readily separable connection between the bit and the holder is even more important. Still further, the nature of the connection between the holder and the bit should be such that the connection can be terminated or established even if the holder and the bit are not readily accessible in an excavation or the like.
In accordance with a presently known proposal, the shank of the bit constitutes an elongated body which is receivable in a chamber of the holder and has a rear end portion provided with a projection receivable in a recess of the holder so that the shank can be pivoted about the projection toward and from a position in which it is properly received in the chamber of the holder. The front portion of the properly inserted shank is thereupon bolted or screwed to the adjacent portion of the holder.
Pivotal mounting of the shank in the holder is not entirely satisfactory because any, even slightest, stray movements of the shank relative to the holder entail pronounced wear upon the shank and upon the adjacent portion of the holder. This allows for additional stray movements and for even more pronounced wear with attendant danger that the shank will leave its chamber or that the head of the bit will break away from the shank.
U.S. Pat. No. 1,140,173 to Levin discloses a bit holder for mining machines wherein the shank of the bit is provided with a row of teeth in each of its lateral surfaces and is received in a narrow chamber of the holder to cooperate with a wedge-like toothed key whose teeth can be placed into mesh with the teeth at one side of the shank. The width of the shank equals its length (as considered in the direction of forward movement of the chain conveyor which carries the bit holder), and the provision of tooth spaces in both sides of the shank entails a pronounced weakening of the shank so that the head of the bit is likely to break away when its cutting edge encounters a pronounced resistance to forward movement.
An additional drawback of the patented bit holder is that the making of teeth and tooth spaces in both sides of the shank of the bit as well as in the key involves a substantial amount of precision work with attendant increased cost of the tool.